Metal cleaning and pickling



Patented Aug. 16, 1938 METAL CLEANING AND PICKLING John V. Vaughen, Lakewood, Ohio, assignor, by

mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing.

Application April 24, 1935,

Serial No. 18,010

16 Claims.

This invention relates to the modification of the action of acids on metals, and is particularly directed to processes and compositions which employ, in conjunction with an acid, an inhibitor comprising unsaturated aldehyde-ammonium sulfide resin.

Pickling and metal cleaning operations frequently involve the use of a bath of dilute, nonoxidizing acids such as sulfuric, hydrochloric, acetic, formic, aqueous solutions of acid sulfates, and the like. Such baths are used for numerous purposes, a typical example of which. is the pickling of iron or steel articles such as wire, sheet, and other manufactures. The composition, concentration, temperature of operation, and other factors vary with difierent baths, but in every instance the primary function of a bath is the removal of undesirable incrustations. As soon as the base metal becomes exposed, it is, in

with consequent damage to the article and with an unnecessary consumption of acid.

' treated inhibitors are quite soluble in pickling- 40 pickled articles.

The application of my invention to acid pickling and acid metal cleaning operations involves no changes in the customary baths and processes, except for the addition of a small amount of one of the inhibitor compositions of this application.

It will, of course, be apparent that my novel inhibitors may be used in numerous other relations as have the inhibitors already known to theart.

I have foundthat the reaction products of unsaturated aldehydes with ammonium sulfides are very eflicient inhibitors. Some of my novel products are rather difliculty soluble, but they can be.

dissolved in pickling baths in the required amount. If treated with 'a' concentrated, non-oxidizing 'mineral acid, these-products become readily soluble and much more efficient, and as such acid baths, they donot introduce suspended material which would be deposited from the baths on This characteristic is particularly advantageous when articles are treated which are subsequently to be subjected to processes, such as enameling or galvanizing, wherein a deposit or stain would be objectionable.

My novel inhibitor compositions, moreover, are completely compatible with the foaming agents ordinarily employed, and, in addition to their inhibiting action, they display a notable foam-producing eificiency themselves.

While any aldehyde may be employed, the unsaturated aldehydes are the most reactive and lead to the production of the most suitable resins for my purposes. The saturated aldehyde, 10!- group, are readily converted into condensation products. Pure aldehydes are quite stable, but it a small amount of a catalyst such as an acid, a base, or a salt be added, the aldehydes' usually polymerize readily, and, in some instances, with almost explosive violence. Some of the aldehyde condensation products are well characterized organic compounds, but usually compounds oi high molecular weight and indefinite composition result, particularly with alkaline catalysts. These latter complex products are difilcult to characterize other than by the term "aldehyde-resinsf. When crotonaldehyde, for instance, is intimately mixed with an aqueous solution of sodium hydroxide, a crotonaldehyde resin forms. The alkali concentration should be in the neighbor. hood of one per cent. Larger amounts of alkali have little additional eiiect and are unnecessary, and, while somewhat smaller amounts may be used, there is a lower limit, oi. about one-tenth per cent, below which resin formation does not occur or is exceedingly slow. The condensation of crotonaldehyde proceeds very rapidly in the presence of sodium hydroxide, and is highly exothermic. Ii allowed to proceed without control, the reaction produces a temperature above 100 C. and hard resins are formed which appear to be partially decomposed by the heatof formation. It is assumed that the alkali salt of hypothetical hydrated aldehyde is formed which breaks down to a form more reactive than the original aldehyde.

Various salts catalyze this type of aldehyde condensation or resin formation, particularly if the salt is one that reacts acidic or alkaline in aqueous solution. In such cases similar products are obtained as if the pure acid or alkali themselves were used. Sodium acetate and sodium carbonate, for instance, are salts which are capable of catalyzing the condensations in question.

The resins formed from crotonaldehyde when ammonia, or ammonium hydroxide are employed as the alkaline catalyst, are quite diflerent from those resulting from crotonaldehyde and sodium hydroxide. With ammonia, or ammonium hydroxide, it appears that at least a part of the crotonaldehyde reacts with the ammonia to form crotonaldehyde-ammonia, which, by reason of the presence of the ammonia as an alkaline catalyst. may then condense with itself and/or with more crotonaldehyde. The crotonaldehyde-ammonia .or. crotonaldehyde-ammonium hydroxide resins contain nitrogen, and are different from the sodium hydroxide resins in acid solubility, odor and appearance.

When acid or alkaline sulfides are employed as a catalyst, condensation products still different in character are obtained. The sulfides act not only to catalyze the condensation but also to introduce sulfur into the resin. The Sebrell Patent No.

1,805,052 of May 12, 1931 suggests as inhibitors the reaction products of aldehydes, such as formaldehyde and aldol, with sulfides, such as hydrogen sulfide, sodium sulfide, and the like. The resins of this patent, of course, contain sulfur.

The Vignos Patent No. 1,843,653 of February 2, 1932, similarly, discusses inhibitors formed by the reaction of aldehydes such as formaldehyde, crotonaldehyde, and benzaldehyde with sulfides. Vignos, moreover, shows ammonia derivatives of the trioladehydes as inhibitors in metal pickling baths. He states that the heterocyclic compound thialdine which is formed by reacting aldehyde ammonia with hydrogensulfide can be used as an inhibitor.

The inhibitors of this application are essentially aldehyde resins which are formed by reacting an unsaturated aldehyde, such as crotonaldehyde, with an ammonium sulfide, such as ammonium sulfide.

The ammonium sulfides act not only as alkaline catalysts for the condensation of unsaturated aldehydes, but, in addition, both the anion and cation of the ammonium sulfides enter into the resin produced. The unsaturated aldehydeammonium sulfide resins are believed to be mixtures .of complex organic compounds of high molecular weight. It seems likely that the resins contain reaction products of aldehyde with ammonia, or ammonium derivative, aldehyde with sulfur, aldehyde with aldehyde, and reaction products of the foregoing with each other, with more aldehyde, and/or with more sulfide or ammonia, or ammonium derivatives. 'Ihe exact chemical constitution of these unsaturated aldehyde-ammonium sulfide resins is not known, but it has been determined that they contain nitrogen and sulfur. It seems probable that both the ammonia, or ammonium derivatives, and the sulfur enter into the combinations, and this hypothesis is strengthened by the fact that equimolecular proportions of reactants lead to the best results.

By employing an ammonium sulfide as a catalyst for the condensation of aldehydes, both the anion and cation, then, are introduced into the resin. The products produced by this simultaneous introduction of sulfur and nitrogen are quite diiferent in properties and character from the above mentioned resins in which the sulfur and nitrogen are introduced one after the other.

It will be readily understood that while the above discussion refers particularly to crotonaldehyde, I do not intend to be limited thereto, and I may use any aldehyde, though preferably those having more than one carbon atom. The best results, however, are obtainable with unsaturated aldehydes. While, more specifically, I have found crotonaldehyde the most satisfactory starting material, it will of course be understood that acetaldehyde and aldol are fully equivalent because in alkaline solution they are readily converted to crotonaldehyde.

While I prefer to use ammonium sulfide itself, any ammonium sulfide may be employed. I may, for instance, use such alkyl or aryl ammonium sulfides as ethylammonium sulfide, di-ethylam-- monium sulfide, tri-ethylammonium sulfide, ethanolammonium sulfide, di-ethanolammonium sulfide, and tri-ethanolammonium sulfide. I may also use such quaternary nitrogen sulfides as pyridinium sulfide, piperidinium sulfide, and quinolinium sulfide. It will be understood from the foregoing that the term ammonium sulfide" is used herein in its generic sense excepting in certain specific instances where reference is made to ammonium sulfide itself.

The aldehyde-ammonium sulfide resins are,

preferably'dispersed or dissolved in some manher and used in such dispersed form. They may be dissolved in a solvent such as acetone, alcohol, ethylene glycol, and the like, or they may be dispersed with such known dispersing agents as sulfite cellulose waste, saponin, or gum arabic.

In order to disperse the aldehyde-ammonium sulfide resins, it is usually preferred to treat them with a concentrated non-oxidizing mineral acid. The resins are dissolved in such acids with a greater evolution of heat than would be expected for mere solution, and I believe that at least a portion of the resin reacts with the acid. I shall, accordingly, designate. the resulting aldehydeammonium sulfide resins as concentrated nonoxitgizing mineral acid dispersion-reaction produc When an unsaturated aldehyde-ammonium sulfide resin is treated with concentrated sulfuric acid, it seems likely that the reaction results in a true sulfation product containing the ROSO3H group, but it may be that a part or all of the product is a sulfonation product. I shall, accordingly, use the term sulfation in a generic sense, as is customary in the art, to include true sulfation and/or sulfonation.

Similarly, the hydrochloric acid dispersion-reaction products of these aldehyde-ammonium sulfide reaction products are of uncertain composition, but the evidence available strongly indicates that they are at least in part a reaction product with hydrochloric acid.

As will be noted in more detail hereinafter, it is sometimes advantageous to treat non-oxidizing mineral acid dispersion-reaction products with an alkali to precipitate the resin.

In order that my invention may be more fully understood, the following illustrative examples are given:

Example I An aldehyde-ammonium sulfide resin was prepared by reacting molecular proportions of crotonaldehyde and ammonium sulfide. The crotonaldehvde was added slowly, and with vigorous stirv.- uuml U01 2 KUWG.

ring, to a twelve and two-tenths per cent solution of ammonium sulfide. A considerable amount of the water constituting the ammonium sulfide solution was present, at first, in the form of ice so as to maintain relatively low reaction temperatures. A white, creamy precipitate was ob- .tained which, on drying in the air, became a white powder which melts at about 60 C.

This product, which constitutes an inhibitor of my invention, was difficulty soluble, but it was found to be a moderately good inhibitor. About 0.005% of the material was dissolved in a hot sulfuric acid pickling bath (5% H2804) by vigorously stirring it in the bath for a considerable time. The attack of the acid on steel was reduced about 92%. If a higher inhibiting eificiency is desired, a larger quantity of the inhibitor may be dissolved in the bath.

The specific nature of the product is greatl influenced by the conditions of the reactions. The

rate of addition of crotonaldehyde to the ammonium sulfide must be adjustedaccording to the I -cedure is quite expensive, and, moreover, the

product is none too satisfactory. The reaction could also be conducted at a boiling temperature, but the product again is none too satisfactory. It is preferred to hold the temperature of reaction below about 20 C. The cooling, obviously, may be accomplished by any desired external or internal cooling means.

The ratio of aldehyde to ammonium sulfide may be widely varied, but the most satisfactory resins are formed when the reactants are used in substantially equimolecular proportions. It will be apparent, also, that while the ammonium sulfide preferably corresponds to the formula (NHOzS, ammonium polysulfldes of difierent ratios of sulfur to ammonia may be used.

The inhibitor of Example I can be dispersed in various ways, if desired. and it may, for instance,,be dissolved in suitable solvents, such as alcohol or acetone. It is advantageously solubilized by dissolving and reacting it with a nonoxidlzingmineral acid. As an example of the procedure followed in preparing a sulfuric acid dispersion-reaction product of an unsaturated aldehyde-ammonium sulfide reaction product, the following is given.

Example II About twenty per cent by weight of the crotonaldehyde-ammonium sulfide resin of Example I was added to an eighty per cent sulfuric acid solution. The reaction was conducted at a temperature of about 90f C. at which temperature 'the resin, of course, is molten. After a time, the

reaction mixture was allowed to cool. The resulting unsaturated aldehyde-ammonium sulfide resin, which is, of course, a dispersion-reaction mixture, constitutes one of the preferred products of my invention, It is a black, viscous liquid which is completely soluble in dilute acids or in water.

When 0.025% by weightof this liquid product was added to a sulfuric acid pickling bath (5% H2804), it reduced acid corrosion 99.2%. Since the liquid was made with 20% of the resin, the 0.025% of this product corresponds to the use of 0.005% of the resin of Example I. It is, then, apparent that the efiiciency was raised from 92% to 99.2% by the sulfation.

In similar studies of the eiliciency of the inhibitors of Example II, it was found that 0.125% of the sulfated inhibitor reduced acid attack about 96.2%, and 0.00625% reduced the acid attack 90.0%.

The specific conditions prevailing in the sulfation-dissolving of the unsaturated aldehydeammonium sulfide reaction product have a considerable efiect on the nature of theproduct. The temperature of the reaction is preferably above the melting point of the resin, but not substantially above about 90 C. At1l0" C., for instance, there is considerable evolution of sulfur dioxide, which, if excessive, may indicate an undesirable oxidation of the resin.

The concentration of the acid may be widelyvaried, but it must not be so dilute that it will not react properly with resin. If the acid is very strong, for instance, greatly above 100%, there is an excessive evolution of sulfur dioxide and the product may be none too satisfactory.

The proportions of acid to resin are not critical, and it is usually preferable to use a rather large excess of acid. Obviously, enough acid must be used to accomplish the desired reaction.

mple 111 An equal weight of the product of Example I was stirred into 95% sulfuric acid. The temperature increased to about 100 C. by reason of the exothermic nature of the reaction. A dark tar-like material was formed, which, after aging at 100 C. for several hours, was quite soluble in water or dilute acids. This material either with or without the aging treatment, constitutes a very satisfactory inhibitor. To produce a dry,

solid aldehyde-ammonium sulfide resin, the prodnot of this example was treated with solid sodium Example IV In order to prepare'a dry inhibitor, the product of Example II was treated with an excess of gaseous ammonia. A precipitate was obtained which, after drying and grinding, was a tan colored powder. the crotonaldehyde resin of Example I in appearance and character. It is more soluble in water or dilute acids, and it is much more eificient as an inhibitor than the original crotonaldehyde-ammonium sulfide resin. When 0.0125% by weight of this powder was added to a five per cent sulfuric acid solution, the acid attack on a steel sheet was reduced about 98%. Under similar conditions, 0.025% of the product of this example reduced the acid corrosion about 99.0%.

It seems probable that the product of this example is at least in part an ammonium salt of the sulfation product of Example II. Such products, obviously, are included under thegeneric This product differs from.

sulfation product present with a consequent,

regeneration of the crotonaldehyde-ammonium sulfide reaction product. Accordingly, I prefer to use weak alkalies, and, more specifically, I prefer to use ammonia in the formation of alkaline salts of the sulfation products.

Example V A product similar to the one produced in Example II was made by reacting about ten per cent by weight of the crotonaldehyde-ammonium sulfide resin in Example I with about ninety per cent of 23 B. hydrochloric acid solution. The reaction was conducted at a temperature of about C. at which temperature the resin, of course, is molten. The product obtained was a liquid very much like the product of Example '11, except that it is lighter in color. When 0.05% of the product of this example was added to a pickling bath, the acid attack was reduced 99.2%.

Example VI Example VII An unsaturated aldehyde-ammonium sulfide resin similar to that of Example I, but employing a different quaternary nitrogen sulfide was prepared by reacting equimolecular proportions of crotonaldehyde and ethanolammonium sulfide. A viscous, greenish liquid product was obtained. This product was poured into water and a yellow, liquid resin precipitated. The resin was found to be quite soluble in dilute acids. Acid attack was reduced, by the use of 0.0125% of the product of this example, 98.25%. If desired, the product of this example may be treated with mineral acids, etc., as in the foregoing examples, but it is readily soluble and does not require further treatment.

While crotonaldehyde is shown in the above examples, other unsaturated aldehydes, such as ethyl hexenal, may be used. As has already been noted, acetaldehyde and aldol are fully equivalent to crotonaldehyde because they are readily converted thereto in alkaline solutions. It will be readily understood that mixtures, particularly commercial mixtures, of aldehydes may be used.

It will be readily understood that the amounts of my inhibitors to housed in a given bath may be widely varied according to the nature of the bath, the inhibiting efliciency desired for a particular purpose, etc. The adjustment of quantitles of inhibitor used can be determined for a particular application by those skilled in the art according to the principles given herein and according to a few typical tests.

The aldehyde-ammonium sulfide resin inhibitors of my invention may be sold in the liquid or dry form as above discussed. As has already been noted, my inhibitors have considerable efllcacy as foaming agents, but if a greater foaming ability is desired, they may be sold admixed with suitable foaming agents, such as sulfite cellulose waste, saponin, soap bark, and gum arabic, with which they are entirely compatible. The inhibitors, and admixtures thereof, can be sold, also, in solution in the acid, or acids, with which they are to be used.

While I have set forth a number of specific processes and specific compositions above, it will be understood that I do not intend to be limited thereby. While I have also advanced certain putative hypotheses regarding the chemical composition of the materials discussed and have ap plied descriptive designations according to such hypotheses, I do not intend to be restricted thereby. I have fully described my invention and have given numerous examples of its application, and the terminology of the claims is to be interpreted in the light of'the specification and restricted only by the prior art.

I claim:

. 1. An inhibitor composition comprising a crotonaldehyde-ammonium sulfide resin.

2. An inhibitor composition comprising a concentrated non-oxidizing mineral acid dispersionreaction product of a crotonaldehyde-ammonium sulfide resin.

3. An inhibitor composition comprising a concentrated sulfuric acid dispersion-reaction product of a crotonaldehyde-ammonium sulfide resin.

4. A composition of matter comprising a product produced by reacting substantially equimolecular proportions of crotonaldehyde and ammonium sulfide.

5. A composition of matter comprising a product produced by reacting, with agitation, substantially equimolecular proportions of crotonaldehyde and ammonium sulfide at a. temperature not substantially higher than 20 C. and then treating the product with a concentrated nonoxidizing mineral acid.

6. A composition of matter comprising a product produced by reacting, with agitation, substantially equimolecular proportions of crotonaldehyde and ammonium sulfide at a temperature not substantially higher than 20 C. and then sulfating with concentrated sulfuric acid at a temperature not substantially higher than 90 C.

'7. In a process of cleaning and pickling metals, the step comprising subjecting the metal to the action of a non-oxidizing acid which contains a product produced by reacting substantially equimolecular proportions of crotonaldehyde and ammonium sulfide.

8. In a process of cleaning and pickling metals, the step comprising subjecting the metal to the action of a non-oxidizing acid which contains a product produced by reacting, with agitation, substantially equimolecular proportions of crotonaldehyde and ammonium sulfide at a temperature not substantially higher than 20 C., and then treating the product with a concentrated nonoxidizlng mineral acid.

9. In a process of cleaning and pickling metals, the step comprising subjecting the metal to the action of a non-oxidizing acid which contains a product produced by reacting, with agitation, substantially equimolecular proportions of crotonaldehyde and ammonium sulfide at a temperature not substantially higher than 20 C., and then sulfating with concentrated sulfuric acid at a 2oz. UUlVH Ubl 1 lUNo. I V

temperature not substantially higher than 90 C.

10. An inhibitor composition comprising a resin prepared by reacting crotonaldehyde with an ammonium sulfide.

11. A metal cleaning and pickling bath comprising a non-oxidizing acid and a resin prepared by reacting an unsaturated aldehyde with an ammonium sulfide.

.12. A metal cleaning and pickling bath comprising a non-oxidizing acid and a concentrated non-oxidizing mineral acid dispersion-reaction product of a resin prepared by reacting an unsaturated aldehyde with an ammonium sulfide.

13. In a process of cleaning and pickling metals, the step comprising subjecting the metal to the action of a non-oxidizing acid which contains a resin prepared by reacting an unsaturated aldehyde with an ammonium sulfide. l

14. In a process of cleaning and pickling metals, the step comprising subjecting the metal to the action of a non-oiddizing acid which contains a concentrated non-oxidizing mineral acid dispersion-reaction product of a resin prepared by reacting an unsaturated aldehyde with an ammonium sulfide.

15. In a process of cleaning and pickling metals the step comprising subjecting the metals to the action of a non-oxidizing acid which contains a resin of the group consisting of resins prepared by reacting an unsaturated aldehyde with an ammonium sulfide, their concentrated non-oxidizing mineral acid dispersion-reaction products, and salts of the dispersion-reaction products.

16. In a process of cleaning and pickling metals, the step comprising subjecting the metal to the action of a non-oxidizing acid which contains a resin prepared by reacting an unsaturated aldehyde with ammonium sulfide.

JOHN VAUGHEN.

Search Room 

